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| United States Patent |
5,328,957
|
|
Sorathia
, et al.
|
July 12, 1994
|
Polyurethane-acrylic interpenetrating polymer network acoustic damping
material
Abstract
Improved acoustic damping materials comprise interpenetrating polymer
netks having a soft polymer component and a hard polymer component. The
soft polymer component, constituting from 50 to 90 percent by weight of
the material, is made by polymerizing an aromatic diisocyanate with a
polyalkylene ether glycol, and the hard polymer component is an acrylic
polymer made by polymerization of the alkyl esters and alkylene diesters
of acrylic and/or methacrylic acid, e.g. n-butyl methacrylate and
tetramethylene glycol dimethacrylate. The curing of the mixture is carried
out at room temperature.
| Inventors:
|
Sorathia; Usman A. (Arnold, MD);
Dapp; Timothy L. (Bowie, MD)
|
| Assignee:
|
The United States of America as represented by the Secretary of the Navy (Washington, DC)
|
| Appl. No.:
|
758972 |
| Filed:
|
August 28, 1991 |
| Current U.S. Class: |
525/123; 525/454; 525/455; 525/903 |
| Intern'l Class: |
C08F 008/30 |
| Field of Search: |
525/123,454,455,903,920
523/400,454
|
References Cited
U.S. Patent Documents
| 3894169 | Jul., 1975 | Miller | 428/317.
|
| 3941725 | Mar., 1976 | Schmittes et al. | 521/116.
|
| 4302553 | Nov., 1981 | Frisch et al. | 525/903.
|
| 4613543 | Sep., 1986 | Dabi | 521/137.
|
| 4766183 | Aug., 1988 | Rizk et al. | 525/454.
|
Primary Examiner: Kight, III; John
Assistant Examiner: Cooney, Jr.; John M.
Attorney, Agent or Firm: Borda; Gary G., Marsh; Luther A.
Goverment Interests
The invention described herein may be manufactured and used by or for the
Government of the United States for governmental purposes without the
payment of any royalties thereon or therefor.
Claims
What is claimed is:
1. An improved acoustic damping material, comprising:
an interpenetrating polymer network having a soft polymer component made of
polyurethane and a hard polymer component made of an acrylic polymer in a
predetermined ratio of soft polymer component to hard polymer component
such that the soft polymer component content is from about 50 to about 90
percent by weight and the hard polymer component content is from about 50
to about 10 percent by weight;
wherein said polyurethane is made by polymerization of an aromatic
diisocyanate and a polyalkylene ether glycol in the presence of
1,4-butanediol and 1,1,1-trimethylol propane, said aromatic diisocyanate
being selected from the group consisting of 4,4'-diphenylmethane
diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and any
mixture thereof, and said polyalkylene ether glycol being selected from
the group consisting of polyethylene ether glycol, polypropylene ether
glycol, and polytetramethylene ether glycol, said polytetramethylene ether
glycol having a molecular weight between about 650 and about 2000; and
wherein said acrylic polymer is made by polymerization of the alkyl ester
of an ethylenically unsaturated carboxylic acid and the alkylene diester
of an ethylenically unsaturated carboxylic acid in the presence of
dimethyl aniline and benzoyl peroxide, said ethylenically unsaturated
carboxylic acid being selected from the group consisting of acrylic acid
and methacrylic acid, said alkyl ester being selected from the group
consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,
isobutyl, tert-butyl, and amyl ester, and said alkylene diester being
selected from the group consisting of ethylene, propylene, and
tetramethylene glycol diester.
2. A process for making an improved acoustic damping material comprising an
interpenetrating polymer network having a soft polymer component made of
polyurethane polymer and a hard polymer component made of acrylic polymer,
comprising the steps of:
measuring in a predetermined ratio the constituents of said soft polymer
component and said hard polymer component, wherein said constituents of
said soft polymer component comprise a polyurethane prepolymer,
1,1,1-trimethylol propane and 1,4-butanediol, and said constituents of
said hard polymer component comprise an alkyl ester of an ethylenically
unsaturated carboxylic acid, an alkylene diester of an ethylenically
unsaturated carboxylic acid, dimethyl aniline and benzoyl peroxide, such
that said soft polymer component content is about 70 percent by weight and
said hard polymer component content is about 30 percent by weight;
in a first vessel, drying and degassing about 100.0 parts of said
polyurethane prepolymer by heating it to 100-110 degrees C. under vacuum;
cooling said polyurethane prepolymer to about 60 degrees C. and adding
about 0.9 parts of said 1,1,1-trimethylol propane with agitation;
cooling the mixture to about 50 degrees C. and adding about 6.3 parts of
said 1,4-butanediol with agitation;
in a second vessel, mixing about 43.9 parts of said alkyl ester of an
ethylenically unsaturated carboxylic acid with about 1.0 parts of said
alkylene diester of an ethylenically unsaturated carboxylic acid, about
0.44 parts of said dimethyl aniline, and about 0.87 parts of said benzoyl
peroxide with agitation;
pouring the contents of the second vessel into the contents of the first
vessel with agitation;
holding the resulting mixture under vacuum for at least eight minutes;
pouring said resulting mixture into a mold; and
letting said resulting mixture cure for about 12 to about 20 hours at room
temperature.
3. A process in accordance with claim 2 in which the polyurethane
prepolymer is made from an aromatic diisocyanate selected from the group
consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, and any mixture thereof, and a polyalkylene
ether glycol.
4. A process in accordance with claim 3 in which the polyalkylene ether
glycol is selected from the group consisting of polyethylene ether glycol,
polypropylene ether glycol, and polytetramethylene ether glycol.
5. A process in accordance with claim 3 in which the polytetramethylene
ether glycol has a molecular weight between about 650 and about 2000.
6. A process in accordance with claim 2 in which the ethylenically
unsaturated carboxylic acid is selected from the group consisting of
acrylic acid and methacrylic acid.
7. A process in accordance with claim 2 in which the alkyl ester is
selected from the group consisting of methyl, ethyl, n-propyl, isopropyl,
n-butyl, sec-butyl, isobutyl, tert-butyl, and amyl ester.
8. A process in accordance with claim 2 in which the alkylene diester is
selected from the group consisting of ethylene, propylene, and
tetramethylene glycol diester.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to polymer compositions, and methods of preparing
them, having improved acoustic damping properties. More specifically, it
relates to polymer mixtures comprising two components, a soft polymer
component and a hard polymer component, which are intimately mixed on a
molecular scale, such mixtures being referred to as "interpenetrating
polymer networks."
2. Description of the Prior Art
Interpenetrating polymer networks having improved acoustic damping
characteristics are known to the art.
U.S. Pat. No. 3,833,404 discloses interpenetrating polymer networks to be
used for surface layers or coatings for damping vibrations or
noise-emitting surfaces. The material consists of poly ethylacrylate
cross-linked with a polyglycol dimethacrylate, and polystyrene
cross-linked with divinylbenzene.
U.S. Pat. No. 4,302,553 discloses a number of interpenetrating polymer
networks having improved tensile strength and swelling properties in
presence of solvents, including combinations of polyurethanes with
polyacrylates, polyepoxides, polyesters, styrene-butadiene polymers and
polydimethyl siloxanes.
U.S. Pat. No. 4,342,793 describes curable resin compositions for protective
surface coatings consisting of interpenetrating polymer networks prepared
from saturated polyols, acrylate and methacrylate esters, and
polyisocyanates, by radiation and thermal curing.
U.S. Pat. Nos. 4,618,658 and 4,719,268 describe polymer modified epoxy
resin compositions comprising the copolymerization product of an epoxy
resin wherein part of the epoxide groups have been modified to provide
polymerizable ethylenic unsaturation; vinyl-terminated urethane oligomer;
and a polymerizable ethylenically unsaturated compound such as styrene or
an acrylate ester.
U.S. Pat. No. 4,742,128 discloses compositions for molded products
consisting of an interpenetrating polymer network comprising a polyamide
and a polyurethane.
U.S. Pat. No. 4,752,624 describes an interpenetrating polymer network for
selective permeation membranes comprising a hydrophilic and a hydrophobic
polymer component. The hydrophylic component is made from hexamethylene
diisocyanate and poly ethylene ether glycol, and cross-linked with
trimethylolpropane. The hydrophobic polymer component is polystyrene
cross-linked with divinylbenzene.
U.S. Pat. No. 4,766,183 discloses a heat-curable composition comprising a
urethane/epoxy/silicone interpenetrating polymer network.
U.S. Pat. No. 4,824,919 describes vinyl ester/styrene composition
flexibilized by the addition of a small amount of polyurethane.
U.S. Pat. No. 4,902,737 discloses a resin having improved impact properties
comprising an aromatic carbonate resin/polyester blend modified by the
addition of a first elastomeric phase of cross-linked polyacrylate, and a
second phase of cross-linked styrene/acrylonitrile.
U.S. Pat. No. 4,923,934 discloses a coating having improved flexibility,
resistance to chemical attack and corrosion, and adhesion, consisting of
an interpenetrating polymer network including a blocked urethane
prepolymer, a polyol, an epoxy resin, and an epoxy catalyst.
U.S. Pat. No. 4,957,981 describes a polymeric material to be used for
optical products such as lenses, goggles, and watch covers comprising an
interpenetrating polymer network of a polyol(allylcarbonate) and an epoxy
resin.
U.S. Pat. No. 4,992,506 provides a molding composition having improved
flexural modulus and softness (lower modulus) comprising an
interpenetrating polymer network of one or more thermoplastic
copolyetheresters, one or more aromatic thermoplastic polyesters, a
rubbery polymer comprising cross-linked (meth)acrylate, and an
interpenetrating cross-linked styrene resin; and, optionally, a mineral
filler.
SUMMARY OF THE INVENTION
The acoustic damping properties of viscoelastic polymeric materials render
them most effective in their glass transition temperature range where the
material changes from hard, glass-like to soft, rubbery consistency. For a
particular polymeric material, the glass transition temperature range is
centered about a characteristic temperature for that material. For most
polymeric materials, the glass transition temperature range is on the
order of 20 degrees C. (see curve labeled 100/0 in FIG. 1). This
temperature range is where the polymeric material provides its maximum
acoustic damping, however, it frequently occurs at temperatures which are
either lower or higher than the temperature range in which a high degree
of acoustic damping is desired from an applications standpoint. Efforts
have therefore been made to broaden the glass transition temperature range
and to shift it to a designated temperature range such that a high degree
of acoustic damping is achieved at temperatures at which acoustic damping
ordinarily is low. The present invention provides a viscoelastic material
interpenetrating polymer network having a broadened glass transition
temperature range and, therefore, improved acoustic damping over a broad
range of temperatures (see curves labeled 70/30, 60/40 and 50/50 in FIG.
1). Furthermore, by adjusting the relative weight percentages of the
polymer components, the temperature range over which maximum acoustic
damping is achieved can be varied to a desired temperature level (see FIG.
1).
The ability of viscoelastic materials to dampen noise and vibration is
related to their complex Young's modulus
E*=E'+iE",
where E' is the real, elastic, or in-phase modulus, and E" is the
imaginary, viscous, loss, or out-of-phase modulus; i=.sqroot.-1. A measure
of the mechanical energy dissipation as heat in a viscoelastic material is
the ratio E"/E', which is also referred to as the damping factor, tangent
delta. It is experimentally determined at 10 Hz with a mechanical thermal
analyzer, such as the Polymer Laboratory Dynamic Mechanical Thermal
Analyzer. All polymer systems exhibit a maximum value for tan delta, and
hence maximum vibration damping, at their glass transition temperature.
Interpenetrating polymer networks are chemically dissimilar cross-linked
polymer chains which have substantially no chemical bonding between them.
They are prepared by allowing two sets of polymer precursors to polymerize
in each other's presence, either simultaneously or sequentially, whereby
two cross-linked polymer networks form which are intimately entangled with
each other on a molecular scale.
It has now been found that, by the choice of appropriate polymer components
and polymer component ratios, interpenetrating polymer networks may be
produced whose glass transition temperature range is broadened and shifted
to a preferred temperature range. Such interpenetrating polymer networks,
as for example the interpenetrating polymer networks of the present
invention, have increased damping factors in the temperature range in
which they are to be used for acoustic damping.
The object of this invention therefore is to provide interpenetrating
polymer networks having novel compositions, broadened glass transition
temperature ranges, and increased acoustic damping factors in designated
temperature ranges. The invention provides a tunable interpenetrating
polymer network acoustic damping material exhibiting superior acoustic
damping properties from a low temperature to a high temperature without
the necessity of changing polymer components for different uses at
different temperatures. A further object of this invention is to provide
processes for preparing such interpenetrating polymer networks.
One component of the interpenetrating polymer networks of this invention is
a soft polymer, and the other component is a hard polymer. The soft
polymer component of the interpenetrating polymer network of this
invention is a polyurethane prepared from one or several diisocyanates and
a polyalkylene ether glycol, cross-linked using a polyol. The
diisocyanates most commonly used are 4,4'-diphenylmethane diisocyanate,
and 2,4 and 2,6-toluene diisocyanate, the latter two most commonly as an
isomer mixture. Polyalkylene ether glycols such as polyethylene ether
glycols, polpropylene ether glycols, and poly tetramethylene ether glycols
may be used, the latter, with a molecular weight between about 650 and
about 2000, being preferred. Polyurethane prepolymers made from aromatic
diisocyanates and polyalkylene glycol ethers may be used. The polyurethane
precursors are polymerized in the presence of their chain extender and
cross-linking agent. As a chain extender, 1,4-butanediol is preferred.
Cross-linking is achieved by the addition of 1,1,1-trimethylol propane.
The hard polymer component of the interpenetrating polymer network of this
invention is made by polymerization of alkyl esters and alkylene diesters
of ethylenically unsaturated carboxylic acids, such as acrylic and
methacrylic acid. Alkyl esters include methyl, ethyl, n-propyl, isopropyl,
n-butyl, sec-butyl, isobutyl, tert-butyl, and amyl esters. Alkylene
diesters include ethylene, propylene, and tetramethylene glycol diesters.
The preferred esters are n-butyl methacrylate and tetramethylene glycol
dimethacrylate. The term acrylic polymer as used herein denotes polymers
made from alkyl esters and alkylene diesters of acrylic and methacrylic
acid, and any mixture thereof.
The acrylic polymer precursors are polymerized in the presence of promoters
and curing agents, such as dimethyl aniline and benzoyl peroxide. The
mixture is then cured at room temperature for 12 to 20 hours, 16 hours
being preferred.
The interpenetrating polymer network of this invention has an extended
glass transition range when the weight percentage of soft polymer
component ranges from 50 to 90, and that of the hard polymer component
ranges from 50 to 10. Broadened glass transition temperature is achieved
by virtue of the acrylic polymer being cross-linked in the presence of
polyurethane, but without chemical interference by the polyurethane, to
produce microphase separation between the polyurethane and acrylic
components. The polyurethane precursors are polymerized in the presence of
their chain extender and cross-linking agent and the acrylic polymer
precursors are polymerized in the presence of their promoter and curing
agent, however, no cross-linking results between the polyurethane and the
acrylic polymer. This result produces a morphology of polymer networks
with microphase domains and entanglement on a molecular scale that produce
broad glass transition temperatures. The results is a polyurethane/acrylic
interpenetrating polymer network having superior acoustic damping
characteristics over a broad temperature range. Thus the invention allows
damping from a low temperature to a high temperature without the necessity
of changing materials for different uses in different temperature ranges.
BRIEF DESCRIPTION OF THE FIGURE
FIG. 1 illustrates the damping factor, tangent delta, as a function of
temperature, for interpenetrating polymer networks according to this
invention as well as that of pure polyurethane and pure acrylic polymer.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In the following detailed description of the preferred embodiments of this
invention, the following abbreviations will be used to identify the
materials used:
M-400, Adiprene M-400, a prepolymer of 4,4'-diphenylmethane diisocyanate
with polytetramethylene ether glycol having a molecular weight of about
1000, Uniroyal Chemicals
BDO, 1,4-butanediol, DuPont
TMP, 1,1,1-trimethylolpropane
NBMA, n-butyl methacrylate monomer, Polysciences
TEGDM, tetramethylene glycol dimethacrylate, Polysciences
DMA, dimethyl aniline, Ashland Chemical
L-98, Lupersol-98, benzoyl peroxide, Lucidol Pennwalt
EXAMPLE 1
This example illustrates the preparation of pure acrylic polymer 25 parts
of NBMA and 0.63 parts of TEGDM are mixed and stirred for about one
minute. 0.26 of DMA are added, and stirring is continued for one minute.
0.5 parts of L-98 are added with vigorous stirring, which continues until
the L-98 has dissolved in the mixture. The mixture is then poured into a
mold and cured at 40 degrees C. for from 12 to 20 hours, 16 hours being
preferred. The damping factor, tan delta, as a function of temperature for
pure acrylic polymer is shown in FIG. 1 as 0/100.
EXAMPLE 2
This example illustrates the preparation of pure polyurethane polymer. 100
parts of M-400 are heated to 100-110 degrees C. and held under vacuum for
an hour to remove moisture and dissolved air. The mixture is cooled to 60
degrees C. and 0.9 parts of TMP are added. The mixture is cooled to 50
degrees C. and 6.3 parts of BDO are added. The mixture is agitated and
held under vacuum for five minutes. It is then poured into a mold and
allowed to cure at room temperature for 12 to 20 hours, 16 hours being
preferred. The damping factor, tan delta, as a function of temperature for
pure polyurethane polymer is shown in FIG. 1 as 100/0. It peaks at about 5
degrees C. and is below 0.2 over most of the temperature range shown.
EXAMPLE 3
This example illustrates the preparation of an interpenetrating polymer
network in accordance with this invention having a soft polymer component
(polyurethane) content of 70 percent by weight. In a first vessel, 100
parts of M-400 are heated to 100-110 degrees C. and held under vacuum for
an hour to remove moisture and dissolved air. The mixture is cooled to 70
degrees C. and 0.9 parts of TMP are added with agitation. The mixture is
cooled to 60 degrees C. and 6.3 parts of BDO are added with agitation,
which continues for at least two minutes.
In a second vessel, 43.9 parts of NBMA and 1.02 parts of TEGDM are combined
with mixing, 0.44 parts of DMA are added with continuing mixing, and 0.87
parts of L-98 are added with further mixing. The contents of the second
vessel are now poured into the contents of the first vessel with vigorous
stirring, and the mixture is held under vacuum for at least eight minutes.
The mixture is poured into a mold and allowed to cure at room temperature
for from 12 to 20 hours, 16 hours being preferred. The damping factor, tan
delta, as a function of temperature for this interpenetrating polymer
network is shown in FIG. 1 as 70/30. It is seen to have a value above 0.2
from about -15 degrees C. to 100 degrees C. The invention, thus, provides
good acoustic damping over a very broad temperature range.
EXAMPLES 4, 5, 6, and 7
Interpenetrating polymer networks having 90, 80, 60 and 50 percent by
weight of soft polymer component (polyurethane) are prepared as described
in Example 3 with the proportions of polyurethane precursors (M-400, TMP,
and BDO) to acrylic polymer precursors (NBMA, TEGDM, DMA, and L-98)
appropriately modified.
Other modifications of this invention will be apparent to those skilled in
the art, all falling within the scope of the invention as described herein
and claimed in the following claims.
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